Prior art radiant heating systems typically employ copper pipe embedded within a concrete slab, or beneath a slab in sand for additional thermal mass. Heated water is circulated through the pipes to transfer thermal energy to the concrete or sand and heat the space above the slab by radiation. Significant disadvantages in systems of this type have been recognized and it is the purpose of the present invention to provide an improved heat exchanger design which overcomes those disadvantages.
Heat transfer systems using copper pipe are subject to corrosion particularly by alkali in the concrete, and thermal expansion and contraction of the pipes and shifting or cracking of the concrete imposes stresses which can cause leaks in the pipe virtually impossible to repair. Concrete has a low rate of heat transfer in comparison to copper and for that reason the use of low temperature water with copper pipe is not economically practical. Copper pipe is quite expensive and the cost of such systems becomes prohibitive unless relatively higher water temperatures are employed.
Perhaps the closest prior art to the tube-stretching inserts of the present invention is Roth U.S. Pat. No. 3,114,969 or Rhinevault U.S. Pat. No. 1,668,978, but neither anticipates the features of the connecting means claimed here. The tube mat per se described below is the subject of U.S. Pat. No. 4,176,654.